Problem with CSS files

[Sorokin-Anton]

If I add a CSS file (e.g. from https://github.com/sindresorhus/github-markdown-css) near template.html and add <link rel="stylesheet" href="github-markdown.css"> to the template.html, the link to the style sheet will be wrong for files in nested folders: e.g. folder/a.md will be transformed to folder/a.html which would have link to folder/style.css which does not exist.

We can expose an option to change href="github-markdown.css" to href="../github-markdown.css" for files in level-1 folders, href="../../github-markdown.css" for level 2, etc